A solid oxide fuel cell (hereinafter also referred to simply as an SOFC) includes a cathode electrode on one side of a solid oxide electrolyte and an anode electrode on the other side.
When oxygen-containing gas such as air is supplied to the cathode electrode and fuel such as hydrogen is supplied to the anode electrode, reaction of oxygen ion with fuel occurs to generate electric power.
A metal catalyst is used for the anode electrode. Oxidation of the metal catalyst may decrease the catalyst activity or cause damage on a fuel cell stack due to a change in volume and the resultant stress.
Patent Document 1 which is WO 2013/001166A discloses applying a current of the opposite direction from that in power generation to a fuel cell when the fuel cell is not in operation, which is intended to prevent oxygen from irreversibly penetrating into a fuel channel to cause oxidation of the metal catalyst of the anode electrode.